Circuits for high-frequency operation of fluorescent lamps



Feb. 14, 1950 J. H; CAMPBELL 2,497,534

cmcurrs FOR HIGH-FREQUENCY OPERATION 0F FLUORESCENT maps Filed Sept; 13, 1947 4- Shee'ts-Sheet 1 aw. /5 M 9 }5 a W 36 v F 35 52 All InvenTor":

John H. CampbeLL, by G kWfiAMW His AH-orneg.

. Feb. 14, 1950 Filed Sept. 1:5, 194? per cenT J. H. CAMPBELL 2,497,534 cxacurrs FOR nrcu-mqusucw OPERATION OF FLUORESCENT LAMPS 4 Sheets sheet Relafive Luminous Lamp eFFiciencg For Inductance, Eesisrance, and Capacity Ballasrs Frequency cgcles per second Invenlrov: John H CampbeLL,

by UM Q;

His A k'iror-neg.

Feb. 14, 1950 J. H. CAMPBELL 2,497,534

CIRCUITS FOR HIGH'FREQUENCY OPERATION OF FLUORESCENT LAMPS Filed Sept. 15, 1947 v 4 sheets-sheets Fi gp 7 '0 '1' E u 1 b ,a acl y a as y lnfiucl-a ce Ballasr no 1/ J/ .IOO

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by UM His Affofn eg.

Feb. 14, 1950 CAMPBELL 2,497,534

CIRCUITS FOR HIGH-FREQUENCY OPERATION OF FLUORESCENT LAMPS Filed Sept. 13, 1947 4 Sheets-Sheet 4 INDGO n5 l/ m F E560 no INDAOO': E ,5 I E3400 3 I g ,j, cAPeo 400' 3 I 1 u 95 -C60 L 0400 y a: R400 12f 9o ,4

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John H. CampbeLL,

His At'lrovneg.

per second or less. the component parts of the control circuit such tities.

pended claims. of an electric discharge device, a frequency changer, and a starting and operating circuit therefore incorporating my invention.

i atenterl Feb. 14, 1950 CIRCUITS Fon HIGH-FREQUENCY OPERA- TION F FLUORESCENT LAMPS John H. Campbell, Mentor Headlands, Ohio, assignor to General Electric Company, a corporation of New York Application September 13, 1947, Serial No. 773,825

6 Claims.

This invention relates to electric discharge devices of the type employing ionzable mediums such as gases or vapors, and more particularly to high frequency circuits for fluorescent lamps.

Circuits now in wide use with fluorescent lamps.-

are designed to operate at a frequency of 60 cycles At this range of frequencies as transformers, reactors and capacitors are heavy, bulky and inefficient. Higher frequency control devices such as are used for fluorescent lamps, however, become smaller in size as the frequency increases, lighter in weight, lower in watt loss, and cost less incomparable production quancuits for a fluorescent lamp suitable for lightweight and more readily portable equipment.

A further object of my invention is to provide new and improved starting and operating circuits for fluorescent lamps for operation within a range of frequencies between 300 and 600 cycles per second, inclusive.

Further features and advantages of my invention will appear from the following description of species thereof. i

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the ap- Fig. 1 is a diagrammatic view Fig. 2 illustrates diagrammatically an electric discharge device, an inverter and a starting and operating;

circuit incorporating my invention. Figs. 3 and 4 illustrate diagrammatically an electric discharge device, a frequency changer and a modification of -the starting and operating circuits of Figs. 1 and 2 incorporating my invention. Fig. 5 illustratesdiagrammatically an electric discharge device with its filamentary electrodes short circuited,

.an inverter and a starting and operating circuit incorporating my invention. Figs. 6, 7, 8 and 9 illustrate graphically the operating characteristics of a 40 watt fluorescent lamp in a circuit incorporating my invention.

Referring to Fig. 1, I have there illustrated one An object of my invention is to provide new and improved starting and operating circuits for an electric discharge device.

Another object of my invention is to provide new and improved starting and operating cit-'20 a rare gas-like neon, argon or mixtures thereof at a pressure of a few millimeters and a small quantity of mercury which, during the operation of the lamps,.has'a low pressure of the order of 10 microns. The device I may be a low pressure positive column lamp of a fluorescent type provided with a suitable phosphor or fluorescent coating. This fluorescent coating upon excitation by the radiation produced by an electric discharge between the electrodes, transforms a shorter wave radiation due to the discharge into longer wave radiation such as radiation within the visible range. For ease of starting a stripe or strip 5 of conductive material which, for example, may be a metallic paint or graphite mixed with potassium silicate, may be applied to the surface of device I. The starting strip 5 may be "connected-to one or both of the electrodes.

In accordance with my invention, device I is connected across a suitable high frequency power 0 supply circuit 6, 6 which, for example, may be supplied from an electronic frequency changer ,l.

. This electronic frequency changer I as disclosed and described in United States Patent 2,288,363,

filed by E. D. McArthur and assigned to assignee of this application may be supplied from a single phase alternating current supply circuit 8 which -may be of commercial frequency such as cycles. The frequency changer system comprises a transformer 9 having a secondary winding it] provided with an intermediate or neutral connection II her or control grid l6. Filtering inductances I1 and [8 are connected in series relation with the associated portions of the secondary winding l0 and electronic discharge device l2 and [3 to prevent the transmission of high frequency current to transformer 9. Electronic discharge device [2 and I3 are of the high vacuum type and corresponding principal electrodes, such as cathodes 15 are connected to the point of reference potential or to the ground. An oscillatory circuit l9 comprising a capacitance 2G and an inductance 2| is coupled to the anodes M of electronic discharge device l2 and I3 through capacitances 22 and 23. The oscillatory circuit [9 is also coupled to control grids I6 of discharge device 12 and I3 through capacitances 24 and 25. The load circuit 26, 26', thatis the starting and operating circuit for the-electric discharge devicel may be energized from the inductance 2! of the oscillatory circuit [9, for instance, by tapping across a por tion thereof.

As a means for selectively increasing the biasing potential impressed on control grids 16 during the negative or inverse half cyclesof. the. anode-cathode voltage of discharge device l2 and I3, a control circuit 21 comprising resistances 28 and 29 and a common connection or injunction 3D is provided. The common injunction 36 is connected to cathodes l of electronic discharge devices 12 and [3 through another resistance 3| which is common to the grid circuits for both discharge devices.

The control circuit 2.! is energized excliisively by grid currents since capacitances 24 and 25 by-pass the high frequency components of current'to ground through the upper portion. of inductance: 2 l

This frequency changer operates to transform the-alternatingcurrent of commercial frequency derived from circuit. 8 into alternating current of a higher frequency. For example, this system may; be employed to supply power at frequencies within the range of 300 to 600 cycles per second, which range. Ihave found to be optimum for circuit and lamp performance, as well as circuit economy. Electronic discharge devices [2 and I3 conduct lowfrequency alternatingcurr'ent alternately during. the periods, or intervals of conduction, of "low frequency. current determined by the voltage of; circuit 8. High frequency excitation is derivedfrom the oscillatory circuit l9 through.

capacitances 24 and 325*and capacitances 22 and The starting and operating circuit 26, 26 for devicei I comprisesz'a'bal-last 32-which serves-as a starting inductancev in serieswith filamentary electrodes of dischargedevice l;.a;switch which, for example; may be'agl'owswitch:33, and filamentary electrode 4- of .dischargedevice l.

preheating to begin. The glow discharge is extinguished' by the bimetallic strip contacting. the center: electrodeia'fi and thus the bimetal cools and in avery short time the contacts formedby.bimetallic strip 35 and center electrode-36' disengage each other." The reduction incurrent flow through the; ballast 32 produces an inductive voltage kick therefrom which is sufficient in-conjunction with theheated electrodes: to cause'an arc dischargeuto. occur between electrodes..-3 and.14. During normal operation, thereLis not enough voltage acrosstheelectric discharge device I to produce further starter switch glowsothe contacts of' the'switchremain open and the starter consumes. no energy."

When the entire installation isenergized by closing-"a :normal mak'e-and-b'rflttk .control switch 31 used: to: connect. the. electronic frequency changer-1 tothe: source. of icurrent 8;. the desired negativepolarity lead;

frequency, namely 300 to 600 cycles per second is supplied to the starting and operating circuit 26, 26'. Current at this frequency then flows through ballast 32, filamentary electrode 3, glow switch 33, and filamentary electrode 4. After a predetermined interval of time the glow switch 33 interrupts the current flow andithe inductive ballast produces-a voltage surge or kick and an arc discharge occurs between the electrodes of discharge device I.

Fig. 2 illustrates diagrammatically a thyratron inverter for supplying frequencies within the range of 300'to 600 cycles per second to a starting and operating circuit therein illustrated embodying asubstantially-exclusive capacitance ballasting arrangement for discharge device I. Fig. 2 embodies thesame corresponding parts of Fig. 1 except electronic frequency converter 1 of Fig. l is replaced by a thyratron inverter 38 supplied by a source of direct current potential 39, and the inductive'ballast'32 is replaced bya: capacitance ballast 40. The-thyratron inverter 38' comprises an inductance-4| connected to'oneside of the direct-current source -39- and to a: center tap .42 of a primary winding 43 of a transformer" 44. The primary winding 43- of transformerv 4'4 is connected'in shunt with anodes 45: an'd-46 of. thyratron tubes-fland 48'. A condenser 49-shunts the anodes 45 and 4 6. Control members'orcontrol grids "50 and 51 ofrthyratron' tubes 4-! and 48,

, polarity; Upon the closingjof 'the manualmake and brealr switch 3'!"current'fiowsathrough the thyratron tube 48, the primary winding; and tothe negative'cp.olarity side of+the direct'current supply. During? this instant of operationthe grid of thyratron tube 4'! is negative and-therefore, will allow no current to'pass-therethrough. Since currentis flowing in a se'ction a: of: the primary winding 43. of transformer; 44; .capacitor 49 is charged 'wlthnlthe potential drop.- Terminal 0 of capacitor 49.is charged with a negative polarity and terminal. 11'; with a positive polarity. Near the;end.of;this. cycle, the? potential to the grids 5| and EOiiSLreVersed: byi means :of: an:- external frequency determining circuit 56 coupled to. the control windingsioroscillator coupling 52. This change has. no immediate effect 1 on the: current flow through-thyratrontube: 48; but allowscurrent to flowthrough thyratronrtube 41, whichin eifect-connects'side d.-. of. the. capacitor to-the This I'GSlllllS'flH asnegative potential on'the an'o'de 46' of 1111108248; thus allowing the :grid 5 of tube I4aito regain control and end the. first half cycle of alternating. current-output. The-same operation repeats in reverse. orderproducingthenext halfcycle. The" frequency of alternating :current output is... determined by the equipment of i this: type is limited. to th crate of dionization oi the thyratron tubes which is approximately 900 cycles per second. Although the above described thyratron inverter functions properly for this type of service other forms of inverters or converters may be used, for. example, a magnetic type frequency converter supplied from either a single phase or three phase 60 cycle supply.

Fig. 3 incorporates the same corresponding parts as described with reference to Fig. 1 except the glow switch 33 is replaced by a condenser 51. The impedance of condenser 5! equals the impedance of ballast 32, thus creating a resonant .type circuit for high frequencies. The voltage created by the resonant condition is of such a value that an arc discharge will not occur be.- tween the electrodes of discharge device I until the electrodes are sufflciently preheated. This starting and operating circuit thus eliminates the need of a starting switch.

Fig. 4 incorporates the same corresponding parts as described in Fig. 3 except the inductive ballast 32 is replaced with a capacitive ballast 58 and the capacitance 51 shunting the electrodes of discharge device I is replaced with an inductance 59. The impedance of the capacitive ballast 58 equals the impedance of the inductance 59.

Fig. 5 incorporates the same corresponding parts as described in Fig. 4 except the electrodes 3 and 4 of discharge device i are short circuited. In this particular case the resonant starting and operating circuit 26, 26' must provide a voltage high enough to produce an arc discharge between electrodes 3 and 4 without preheating the electrodes.

Figs. 6, '7, 8 and 9 illustrate graphically the operating characteristics of a 40 watt fluorescent lamp in a circuit incorporating my invention. The 40 watt lamp was chosen as an example in plotting the above curves because it is produced in large quantities and is in general use for industrial lighting where large high frequency converters would offer the greatest advantage. When similarly plotted, data taken on lamps of other sizes show approximately the same curve shapes as do those taken on the 40 watt lamp.

Lamp characteristics are considerably affected by the type of ballast employed to control the arc discharge in an electric device. In order to point out these differences, the three fundamental types of ballasts, namely, inductance, capacitance and resistance, are used. Curves giving the luminous lamp efficiency and overall circuit efiiciency for each type of ballast is shown in Figures 6 and '7. All curves are plotted in percentage of 60 cycle characteristics.

Fig. 6 shows graphically the relationship of the efficiency of a 40 watt lamp with varying frequency for the three types of ballasts. The percentage lamp efficiency is plotted against frequency using efficiency of a lamp operated on an inductive ballast at 60 cycles as 100%.

Inductive ballasts can be made smaller as frequency increases, but as the frequency rises, it may be necessary to use a higher grade iron for the core in order to avoid excessive losses due to core saturation. This results in a relatively expensive design and therefore the reduction in size appear to be practical for frequencies much below 300 cycles because of the adverse effect on lamp characteristics at lower frequencies. However, at frequencies above 300 cycles, this method of control has many advantages among which are the relatively small size, light weight, low cost and low losses. The small capacitance required to ballast a 40 watt lamp at high frequency makes possible the design of a single lamp ballast of comparatively small dimensions and weights ranging in ounces instead of pounds.

In any economic consideration, the overall efficiency of the circuit must be taken into account to determine actual operating costs. The curves in Fig. '7 show the overall efliciency for inductance, capacitance and resistance ballasts. Since inductance is the most commonly used, this method of ballasting at 60 cycles is indicated to represent the point. All other curves are therefore in percentage of this base. The rapid rise of overall efficiency in the case of the capacitor ballast is accounted for in the improvement of wave shape and the low loss of this method of ballasting at higher frequencies. The inductance is fundamentally higher in loss and therefore remains less efiicient over the frequency range shown. The lower resistance curve shows little improvement in overall efliciency when design for the same line voltage (200 volts) as the two other types of ballasts. The change from 53% to 56% over the range of 60 to 600 cycles is due entirely to the gain in lamp efficiency. The upper resistance curve indicates the overall efiiciency with the ballast design for lower line voltage at points where good regulation and lower lamp operating voltage is permitted.

Fig. 8 shows the lamp characteristics for a capacitance type ballast. At the lower frequencies such as 60 cycles, this method of control is impractical due .to the delay of the capacitor in allowing current to flow through the lamp. The lamp conducts current for a relatively short period each half cycle, resulting in low lamp emciency and pronounced stroboscopic effect. At the higher frequencies the current wave shape improves and lamp efiiciency approaches that of an inductive ballast. At approximately 300 cycles the lamp efficiency using a capacitor ballast is the same as that of an inductively ballasted lamp operating at 60 cycles. More important than lamp efficiency is the gain in overall efiiciency of the circuit when a capacitor ballast is used. Fig. 7 shows this relationship. It will be noted that a capacitor ballast operating in the range of 300 to 600 cycles provides an overall efficiency from 17% to 22% greater than that provided by an inductive ballast at 60 cycles.

The regulation of lamp watts and light output with changes in line voltage is shown in Fig. 9. The curves show percentage lamp watts with a 10% change in line voltage for the three types of ballasts on both 60 and 400 cycle power. It will be noted that regulation improves with frequency for inductance and resistance type ballasts. However, since series capacitance provides more nearly constant current with changes in voltage the regulation of the capacitance curve is superior to inductance or resistance at both frequencies. Thus, the capacitance ballast operating between the frequency range of from 300 to 600 cycles per second has a regulation superior to inductance or resistance ballasts. Although I have described my invention with reference to single electric discharge device circuits, it may be readily ap meme-1i it? plied tocircuitwniploying a. plurality of: devices;

What I claim as anew. and. desire. to secure by Letters Patent of the United States. is:

1'. In combination, an electric discharge device of the type employing 'an' ionizableamedium and comprising a plurality of. filamentary electrodes and ballast means consisting-of a. substantially exclusively. capacitiverreactance. in :series with said device across a' source of current having a frequencyof the order of several hundred cycles perv second butxgreater. than about 300 cycles per second;

2. In combination, an-electric discharge device'of the type: employing an ionizable medium and comprising a plurality of' electrodes and ballast means consisting of a substantially. exclusively capacitive reactance in series with said device across a source of current having afrequency within-the range of 300 to 600 cycles per. second, inclusive.

3-. In combination, an electric discharge device of the type'employing-an ionizable medium and: comprising aplurality ofv filamentary electrodes, an alternating current supply circuit, a frequency changer across saidsupply circuit for converting the suppl to current having a frequency in the range-of about 300 to 600 cycles per" second, and ballast means consisting of a substantially exclusively capacitive reactance, said capacitive reactance being connected in series with saidd'evice and'across said frequency changer.

4. In combination, an electric discharge device of the'type employing anionizable medium and comprising a-pl-urality of electrodes atleast one of which is of 'thefilanientary type, ballast means consisting of awsubstantia'lly exclusively capacitive reactance inv series with said discharge device across :a source of current having aifrequencyw-ithin the rangeof 300t'o 600 cycles per second, and a starting me'ans in series with 8 saidaelectrodes and shunting said device-ibuproviding starting current 5. In combination, a gaseous electric. discharge device having at least onerfilamentary electrode and. aflcooperating electrode, ballast means consistingof a substantially exclusively capacitive reactance in series with said discharge device acrossva source of current having afrequency within the range of 300to 600 cycles perxsecond; andsan inductivereactance in series w-ith saidelectrodes :and shunting said device for providing; optimum. starting voltage;

6; In combination, an electric discharge device of the 1 type. employing: an ionizable. medium andc'omprising aplurality of electrodes, ballast means: consisting ofia substantially exclusively capacitiveireactan'cetin series witlisaid discharge device across a source ofcurrent having a: frequency'w-ithinthe range: of 300 to 600 cycles per second, and an: inductive: reactance connectedv across said. electrodes and constituting with said capacitive reactance a resonant circuit for providing optimum starting voltage.

JOHN H. CAMPBELL.

REFERENCES CIT-ED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,050,135 Tour Aug. 4, 1936 2,0561629 Uyterhoeven et al. Oct. 6, 1936 2086, 668 'Fod'or July 13, 1937 2,133,494 Water's Oct-18, 1938 2,170,447 Edwards Aug. 22, 1939 2,284,407 Edwards May 26, 1942 "2301,671' Abadie Nov. 10, 1942 2,368,090 Abernathy Jan. 30, 1945 '2,'4-23;03'1 'Kurtz et a1 June 24, 1947 

